Apparatus and method of improving impedance matching between an RF signal and a multi- segmented electrode

ABSTRACT

An apparatus and method of improving impedance matching between a RF signal and a multi-segmented electrode in a plasma reactor powered by the RF signal. The apparatus and method phase shifts the RF signal driving one or more electrode segment of the multi-segmented electrode, amplifies the RF signal, and matches an impedance of the RF signal with an impedance of the electrode segment, where the RF signal is modulated prior to matching of the impedance of the RF signal. The apparatus and method directionally couples an output of the matching of the impedance of the RF signal and the electrode segment, and adjusts the output of the matching of the impedance of the RF signal such that a directionally coupled output signal and a reference signal representing the RF signal at the output of the master RF oscillator produces a demodulated signal of minimal amplitude.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of PCT InternationalApplication No. PCT/US02/05588, filed Feb. 27, 2002, which claimspriority to U.S. Provisional Application No. 60/272,454, filed Mar. 2,2001. The entire contents of these prior applications are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method ofimproving impedance matching between an RF signal and a multi-segmentedelectrode in a plasma reactor powered by the RF signal.

2. Discussion of the Background

Manufacturers of semiconductor integrated circuits (IC) are faced withsevere competitive pressure to improve their products. This pressure inturn is driving the manufacturers of the equipment used by ICmanufacturers to improve the performance of their equipment. Oneparticular type of tool that is widely used, and that is thereforeparticularly susceptible to these competitive pressures, is the plasmareactor. These reactors can be used to remove material, or, withmodifications, the reactors can be used to deposit material. Themechanisms for either deposition or removal are complex, but in eithercase, it is essential to control the physical processes at the surfaceof the wafer. Control of these processes is the focus of significanttechnological development.

One of the key factors that determine the yield and overall quality ofan IC is the uniformity of processes, such as etching, at the surface ofthe wafer. In plasma reactors, uniformity is governed by the design ofthe overall system, and in particular by the design of the RF feedelectronics and the associated control circuitry.

SUMMARY OF THE INVENTION

The inventors have recognized that one important method of providing auniform process involves measuring inter-electrode coupling in plasmareactors with multi-segmented electrodes, and adjusting the processaccordingly. The inventors have identified various difficulties inmeasuring the inter-electrode coupling in plasma reactors, as will bedescribed in detail below, and the inventors have provided an apparatus.Thus, a method is intended to address these difficulties and improveimpedance matching between an RF signal and a multi-segmented electrodein a plasma reactor powered by the RF signal.

An embodiment of the present invention advantageously provides anapparatus that includes an electrode segment adapted to be connected tothe RF signal by a circuit. The circuit includes a phase shifter adaptedto be connected to the RF signal, an amplifier connected to an output ofthe phase shifter, and a matching network connected to an output of theamplifier, where the matching network is configured to match animpedance of the RF signal with an impedance of the electrode segment.The circuit further includes a modulation source configured to modulatethe RF signal prior to receipt by the matching network, a directionalcoupler connected to an output of the matching network and having anoutput connected to the electrode segment, and a demodulator configuredto receive an output signal from the directional coupler and a referencesignal representing the RF signal at the output of the master RFoscillator. The circuit also includes a control system connected to anoutput of the demodulator, where the control system is configured tocontrol the output of the matching network such that the output signalof the demodulator is minimized.

The apparatus preferably provides that the modulation source isconnected to an input terminal of the phase shifter, or, alternatively,the modulation source is connected to an input terminal of theamplifier. The apparatus preferably provides that the modulation sourceis adjustable. In alternative embodiments, the reference signal isreceived by the demodulator from the output of the master RF oscillator.In alternative embodiments, the demodulator is synchronous, or thedemodulator is asynchronous (non-synchronous). The apparatus preferablyprovides that the control system is configured to control the phaseshifter and the amplifier. The apparatus preferably includes a filterconnected to an output of the directional coupler, where the filter hasan output connected to the electrode segment.

The apparatus preferably further includes an additional electrodesegment adapted to be connected to the RF signal by the circuit. Thecircuit further includes an additional phase shifter adapted to beconnected to the RF signal, an additional amplifier connected to anoutput of the additional phase shifter, an additional matching networkconnected to an output of the additional amplifier. The additionalmatching network is configured to match an impedance of the RF signalwith an impedance of the additional electrode segment, and themodulation source is selectively configured to modulate the RF signalprior to receipt by the additional matching network. The circuit furtherincludes an additional directional coupler connected to an output of theadditional matching network, where the additional directional couplerhas an output connected to the additional electrode segment. Thedemodulator is configured to selectively receive (1) an output signalfrom the additional directional coupler and (2) an additional referencesignal representing the RF signal at the output of the master RFoscillator. The control system is configured to control the output ofthe additional matching network such that the output signal of theadditional demodulator is minimized.

An alternative embodiment of the apparatus preferably includes anadditional electrode segment adapted to be connected to the RF signal bythe circuit. The circuit includes an additional phase shifter adapted tobe connected to the RF signal, an additional amplifier connected to anoutput of the additional phase shifter, an additional matching networkconnected to an output of the additional amplifier, where the additionalmatching network is configured to match an impedance of the RF signalwith an impedance of the additional electrode segment, an additionalmodulation source configured to modulate the RF signal prior to receiptby the additional matching network, and an additional directionalcoupler connected to an output of the additional matching network, wherethe additional directional coupler has an output connected to theadditional electrode segment. In this embodiment the demodulator isconfigured to receive an output signal from the additional directionalcoupler and an additional reference signal representing the RF signal atthe output of the master RF oscillator, and the control system isconnected to the output of the demodulator, where the control system isconfigured to control the output of the additional matching network suchthat the output signal of the additional demodulator is minimized.

The apparatus of the present invention is preferably incorporated into aplasma reactor including a process chamber; a multi-segmented electrodewithin the process chamber, and an RF power supply system configured togenerate an RF signal to drive an electrode segment of themulti-segmented electrode, where the circuit connects the electrodesegment to the RF signal.

The present invention further advantageously provides a method includingthe steps of phase shifting the RF signal driving an electrode segmentof the multi-segmented electrode, amplifying the RF signal, and matchingan impedance of the RF signal with an impedance of the electrodesegment, where the RF signal is modulated prior to matching of theimpedance of the RF signal. The method further includes the steps ofdirectionally coupling an output of the matching of the impedance of theRF signal and the electrode segment, and adjusting the output of thematching of the impedance of the RF signal such that a directionallycoupled output signal and a reference signal representing the RF signalat the output of the master RF oscillator produces a minimized outputsignal from the demodulator.

The method preferably provides that the step of adjusting the output ofthe matching of the impedance of the RF signal includes the steps ofdemodulating the directionally coupled output signal and the referencesignal, and controlling the output of the matching of the impedance ofthe RF signal such that the demodulated directionally coupled outputsignal is minimized. In alternative embodiments, the RF signal is phasemodulated prior to matching of the impedance of the RF signal, or the RFsignal is amplitude modulated prior to matching of the impedance of theRF signal. Further, in alternative embodiments, the reference signalrepresents a RF signal output from the master RF oscillator. The methodpreferably includes the step of filtering the RF signal after the RFsignal is directionally coupled and before the RF signal is received bythe electrode segment.

The method preferably includes the steps of phase shifting an additionalRF signal driving an additional electrode segment of the multi-segmentedelectrode, amplifying the additional RF signal, matching an impedance ofthe additional RF signal with an impedance of the additional electrodesegment, where the additional RF signal is modulated prior to matchingof the impedance of the additional RF signal, directionally coupling anoutput of the matching of the impedance of the additional RF signal andthe additional electrode segment, and adjusting the output of thematching of the impedance of the additional RF signal such that anadditional directionally coupled output signal and an additionalreference signal representing an additional RF signal at the output ofthe master RF oscillator prior to modulation produce a minimized signalat the output of an additional demodulator. In alternative embodiments,the RF signal and the additional RF signal are selectively modulatedusing a single modulation source, or the RF signal and the additional RFsignal are modulated using independent modulation sources.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will become readily apparent with reference to thefollowing detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

FIG. 1 is an electrical equivalent circuit representing electricalconnections to electrode segments and inter-electrode couplingimpedances for a five-electrode reactor;

FIG. 2 is a schematic representation of a plasma reactor systemaccording to the present invention;

FIG. 3 is a diagram of an embodiment of the present invention depictinga phase modulation circuit with a single modulation source for theelectrode segments;

FIG. 4 is a diagram of an alternative embodiment of the presentinvention depicting an amplitude modulation circuit with a singlemodulation source for the electrode segments;

FIG. 5A is a diagram of an embodiment of the present invention depictinga phase modulation circuit with independent modulation sources for eachelectrode segment;

FIG. 5B is a diagram describing an array of filters to be used with theembodiments presented in FIGS. 5A and 6; and

FIG. 6 is a diagram of an alternative embodiment of the presentinvention depicting an amplitude modulation circuit with independentmodulation sources for each electrode segment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors have identified problems with conventional processingreactors and methods of using those reactors that are solved by thepresent invention. Therefore, the present invention provides anapparatus and a method for improved impedance matching between an RFsignal and a multi-segmented electrode in a plasma reactor powered bythe RF signal which overcomes the shortcomings identified with regard tothe conventional processing reactors.

The inventors recognized the difficulty in measuring the inter-electrodecoupling in plasma reactors with multi-segmented electrodes. There isconsiderable coupling between the electrodes of plasma reactors withmulti-segmented electrodes. The coupling is due to mutual capacitancebetween the electrodes, mutual lead inductances, imperfect isolationbetween the RF generators that drive each electrode, and couplingbetween the matching networks. However, when the reactor is energizedand plasma is present, the coupling between the electrodes increasesdramatically due to the presence of the plasma. Thus, measurements ofthe coupling between electrodes that are made when the reactor is notoperating are not valid when the reactor is being used and there isplasma present. What is needed is a way to measure the coupling betweenelectrodes in plasma reactors with multi-segmented electrodes in orderto facilitate the achievement of improved impedance matching for eachelectrode.

The difficulty is measuring the inter-electrode coupling in plasmareactors with multi-segmented electrodes while the process evolves. Asthe process conditions in the reactor change during use, the couplingbetween the electrodes also changes. What is needed is a way to measure,as a process proceeds, the changes in the coupling between theelectrodes that routinely occur during normal reactor use as aconsequence of electrode erosion, process changes, etc. Similarly, forthe application of RF power to an electrode with a consistent impedancematch, the ability to differentiate the contributions to a measured RFsignal at the electrode from inter-electrode coupling and plasmareflections of the signal applied to the electrode provides aconsiderable advantage for repeatable process conditions.

Additionally, it is important to measure the inter-electrode coupling inplasma reactors with multi-segmented electrodes without interfering withthe process. Plasma based process dynamics are sensitive to parasitic orstray capacitances and inductances whose impedances depend on processparameters. Thus, a change in the plasma due to a measurement affectsthe process, which can adversely affect the performance of the reactor.What is needed is a way to measure the inter-electrode coupling inplasma reactors with multi-segmented electrodes without interfering withthe process. The method is based on modulating, in a way that is benignto the process, the RF signal being used to power the electrodes, andafterwards demodulating the ensuing signal.

FIG. 1 depicts an electrical equivalent circuit that represents theelectrical or electrode connections 10 to the electrode segments, S₁,S₂, . . . S₅ for a five-electrode system, and the twenty (although onlyten are shown) interelectrode coupling impedances Z₁₂, Z₁₃ Z₁₄, Z₁₅,Z₂₃, Z₂₄, Z₂₅, Z₃₄, Z₃₅, and Z₄₅ (Z₂₁, Z₃₁, Z₄₁, Z₅₁, Z₃₂, Z₄₂, Z₅₂,Z₄₃, Z₅₃, and Z₅₄ are not depicted). In general there may be fewer thanor greater than five electrodes. For an N electrode system, theimpedances Z_(ij), where i,j=1, 2 . . . N, subject to the condition thati is not equal to j, represent the inter-electrode coupling impedances.For the case considered above, N=5. For a linear circuit Z_(ij)=Z_(ji),and, in general, the total number of inter-electrode coupling impedancesis N(N−1)/2. Thus, for an electrode with more than 3 segments, thenumber of unknown coupling parameters is larger than the number ofaccessible terminals, and the segments, in general, have to be excitedin N(N−1)/2 different ways to determine all of the interactions, unlessthe symmetry of the segmented electrode would allow one to infer thatcertain inter-electrode impedances are equal. For a non-linear circuit,the total number of inter-electrode coupling impedances is N(N−1). Whatis needed is a way to measure the inter-electrode coupling in plasmareactors with multi-segmented electrodes or a plurality of electrodes.

It is even more difficult to measure the inter-electrode coupling inplasma reactors with multi-segmented electrodes when there arenon-linear elements present in the network. The presence of thenon-linear plasma introduces significant added complexity to the problemof determining the inter-electrode coupling in plasma reactors withmulti-segmented electrodes. This complexity is significantly less thanit once was because of tremendous advances that have been made inunderstanding the dynamics of non-linear systems. However, even now onlysimplified cases usually lend themselves to analysis. Such cases oftenlack the generality of plasma systems as a whole, and actualcommercially available plasma reactors in particular. What is needed isa way to measure the inter-electrode coupling in actual plasma reactorswith multi-segmented electrodes when non-linear elements are present inthe RF network.

The preferred embodiment of a plasma reactor system for processing asubstrate or wafer according to the present invention is depicted inFIG. 2. The system generally includes a plasma chamber 20 that containstwo or more capacitively-coupled, electrode segments 22 and a waferchuck 14 for supporting a wafer 16, and a wafer handling and roboticssystem 24 that moves wafers into and out of the plasma chamber 20. Thesystem further includes a multiple segment inject electrode RF powersupply system 26 that includes separate RF generation systems to driveeach segment 22 of the segmented upper electrode and an inter-electrodecoupling impedance measuring capability, and a cooling system 28 thatcirculates a coolant through coolant lines 30 and 32 to and from anenclosed cooling chamber 34 that is part of the plasma chamber 20. Thesystem also includes a vacuum pump system 36, a gas supply system 38that delivers gas to the plasma chamber 20, and a control system 40 thatoversees the operation of the tool and the interactions of the variousparts. The RF power supply system 26 includes a separate RF generationsystem to drive each segment 22 of the upper electrode.

FIG. 3 is a diagram of an embodiment of the present invention depictinga phase modulation circuit with a single modulation source for theelectrode segments. The embodiment of FIG. 3 is based on phasemodulation with a drive electrode having three segments. In general, theelectrode may include any number of segments, N. In the discussion ofFIG. 3 that follows, the uppermost electrode segment is referred to aselectrode segment A. The circuit associated with electrode segment A,which is denoted by 160A in FIG. 3 (and denoted generally by 22 in FIG.2), will be described. The circuits associated with the remaining N−1electrode segments (two additional electrode segments are depicted inFIG. 3) are identical, and corresponding circuit elements are denoted bythe same number with an appropriate letter appended after the number(for example, 160A, 160B, and 160C). All of the electrode segments areimmersed in plasma 270.

A master RF oscillator 105 from within the RF power supply system 26(see FIG. 2) provides a common RF signal as the input for the drivecircuit for each electrode segment. The power output and frequency of RFoscillator 105 is to be compatible with phase shifters 110, amplifiers130 and de-modulator 140. The RF oscillator preferably has a frequencyof 60 MHz, but other frequencies can alternatively be used. The poweroutput of the amplifiers 130 is preferably on the order of hundreds ofwatts.

With regard to the drive circuit for electrode segment 160A, the outputof RF oscillator 105 is electrically coupled to the input terminal ofvoltage-controlled phase shifter 110A. The phase difference between theRF voltage at the output terminal of voltage-controlled phase shifter110A and the RF voltage at the input terminal of voltage-controlledphase shifter 110A is controlled by the sum of the output voltages ofphase controller 112 and modulation source 120, both of which areelectrically connected to the phase control terminal of phase shifter110A by means of a summer or adder (not depicted). The phase differenceis variable over a range of 2π radians or, equivalently, 360°.

The frequency and amplitude of modulation voltage source 120 areadjustable, however a frequency in the range from about 1 kHz to 10 kHzis preferred. The amplitude of the output voltage of modulation source120 determines the amplitude of the AC phase variation produced by phaseshifter 110 to which it is electrically connected. The modulation source120 can be electrically connected to any of the phase shifters 110 byusing a selector switch 175 (e.g., a ganged selector switch. FIG. 3depicts modulation source 120 connected by the selector switch 175 tophase shifter 110A. The selector switch 175 alternatively can be anelectronically controlled device, rather than a mechanical device asdepicted in FIG. 3. The output terminal of phase shifter 110A iselectrically coupled to the input terminal of voltage-controlled RFamplifier 130A. The control terminal of voltage-controlled RF amplifier130A is electrically coupled to the output terminal of gain controller125. The output voltage of gain controller 125 controls the gain of thevoltage-controlled RF amplifier 130A.

The output of voltage-controlled RF amplifier 130A is electricallycoupled to match network 135A, which automatically matches the inputimpedance presented by the electrode segment 160A at the frequencydetermined by RF oscillator 105 by a match controller 170, and theoutput of matching network 135A is electrically connected to the powerinput port 146A of directional coupler 145A. The power output port 147Aof directional coupler 145A is electrically connected to the inputterminal of low-pass (or band-pass) filter 150A, which is intended toprevent power generated in the plasma at any harmonics of the RFfrequency produced by RF oscillator 105 from reaching match network135A. Finally, the output terminal of low-pass (or band-pass) filter150A is electrically connected to electrode segment 160A.

The amount of RF power emerging from electrode segment 160A is directedvia terminal 148A of directional coupler 145A to one terminal of aswitch 185. In fact, the RF signal emerging from terminal 148A ofdirectional coupler 145A is an attenuated RF voltage comprising a firstcomponent associated with the reflection of the RF signal incident onthe power coupling structure (i.e. electrode 160A) as well as additionalRF components associated with the coupling of RF power betweenelectrodes within the multi-electrode system. The switch 185 canalternatively be an electronically controlled device, rather than amechanical device as depicted in FIG. 3. Corresponding terminals 148 ofdirectional couplers 145 are electrically connected, respectively, tocorresponding terminals of switch 185. By actuating the switch 185, theRF power emerging from any electrode 160 may be connected to the inputterminal 195 of synchronous demodulator 140. FIG. 3 depicts electrodesegment 160A connected by the switch 185 to the input terminal 195 ofsynchronous demodulator 140.

The reference terminal 190 of synchronous demodulator 140 is alsodepicted in FIG. 3 as electrically connected to the output of the masterRF oscillator 105. Although the demodulator of this embodiment is asynchronous demodulator 140, a simpler nonsynchronous demodulator may beused instead, albeit with somewhat reduced immunity to noise. Inaddition, the amount of RF power incident upon electrode segment 160Afrom match network 135A may be measured at terminal 180A of directionalcoupler 145A (by a detection system not depicted).

One such demodulator 140 could be an I-Q demodulator, wherein provided aRF input 195 and a local (reference) oscillator input 190, it outputstwo signals at the modulation frequency, namely, I(t)=I cos(ω_(m)t) andQ(t)=Q sin(ω_(m)t), where ω_(m) is the modulation frequency. Theamplitudes I and Q may be used to compute (I²+Q²)^(1/2) which isproportional to the desired power to be measured. When, for instance,selector switch 175 is set such that the RF signal incident on electrode160A is phase-modulated and selector switch 185 is set such that itreceives a RF signal from output 148A of directional coupler 145A, thenthe output (described above) from demodulator 140 is proportional to theRF power associated with the reflections of the corresponding RF powerincident at electrode 160A through match network 135A (and measured atnode 180A). Furthermore, while keeping the selector switch 175unchanged, selector switch 185 may be changed to receive the RF signalfrom output 148B of directional coupler 145B and then the output fromdemodulator 140 is proportional to the power coupled from electrode160Aa to electrode 160B. Similarly, this may be carried out through theNth electrode. Therefore, by carrying out this operation for eachelectrode, one may obtain N² outputs which, in addition to monitoringthe reflected incident power at each electrode (N signals), one alsoprovides sufficient information (the remaining N(N−1) signals) tounderstand the coupling between electrodes of a N-electrode system asdescribed in FIG. 1.

Moreover, the output from the demodulator 140 (as described above) canbe calibrated (if necessary) by performing the N² measurements describedabove while only delivering RF power to a single electrode. For example,phase-modulated RF power is delivered to a first electrode (in themulti-electrode system) while sequentially recording the output fromdemodulator 140 for each selector switch 185 setting (i.e. eachelectrode) and, using a second directional coupler and detector (notshown) in line with the first directional coupler 145, sequentiallyrecording the power emerging from the respective electrode 160 in adirection from the electrode 160 to the match network 135. Simply byincreasing the power to the given electrode, one may increase thereflected power and power coupled to other electrodes, wherein acalibration curve for the output of demodulator 140 and power can beassembled. This sequence of measurements is then performed for each ofthe remaining electrodes. Moreover, the calibration may be repeatedwhile delivering power to multiple electrodes to check the significanceof nonlinear effects.

Finally, a processor or computer 200 controls, by using appropriatesoftware, a phase controller 112, a gain controller 125, a matchcontroller 170, and, preferably, switches 175 and 185. Input to thecomputer 200 by an operator is affected by an input device 250, whichis, for example, a keyboard or a touch-sensitive screen. The computer200 includes a computer monitor 260, upon which data obtained by themeasurement system is displayed. In one embodiment, the computer 200 mayserve to provide the match network controller with the above-mentionedinformation, particularly the measurement of the reflected incidentpower at each electrode. In turn, the match network controller may beprogrammed to minimize the reflected incident power at each electrodeand serve the purpose of providing a repeatable plasma process using themulti-electrode system. Similar to controllers in the prior art, thissystem provides information on the forward and reflected incident powerat each electrode in a multi-electrode configuration to the controlalgorithm of the match network controller.

FIG. 4 is a diagram of an alternative embodiment of the presentinvention depicting an amplitude modulation circuit with a singlemodulation source for the electrode segments. The embodiment depicted inFIG. 4 is based on amplitude modulation with a drive electrode havingthree segments. In general, the electrode may include N segments. In thediscussion of FIG. 4 that follows, the uppermost electrode segment isreferred to as electrode segment Aa. The circuit associated withelectrode segment A, which is denoted by 160A in FIG. 4 (and denotedgenerally by 22 in FIG. 2), will be described. The circuits associatedwith the remaining N−1 electrode segments (two additional electrodesegments are depicted in FIG. 4) are identical, and correspondingcircuit elements are denoted by the same number with an appropriateletter appended after the number.

A master RF oscillator 105 from within the RF power supply system 26(see FIG. 2) provides a common RF signal as the input for the drivecircuit for each electrode segment. The power output and frequency of RFoscillator 105 is compatible with phase shifters 110, amplifiers 130 anddemodulator 140. The RF oscillator 105 has a frequency that ispreferably 60 MHz, but other frequencies are possible. The power outputof the amplifiers 130 is preferably on the order of hundreds of watts.

With regard to the drive circuit for electrode segment 160A, the outputof RF oscillator 105 is electrically coupled to the input terminal ofvoltage-controlled phase shifter 110A. The phase difference between theRF voltage at the output terminal of voltage-controlled phase shifter110A and the RF voltage at the input terminal of voltage-controlledphase shifter 110A is controlled by the output voltage of phasecontroller 112 which is electrically connected to the phase controlterminal of phase shifter 110A. The phase difference is variable over arange of 2π radians or, equivalently, 360°. The output terminal of phaseshifter 10A is electrically connected to the input terminal ofvoltage-controlled RF amplifier 130A.

The modulation source 120 may be electrically connected to any of thevoltage-controlled RF amplifiers 130 by a selector switch 175. Thefrequency and amplitude of modulation voltage source 120 are adjustable,however a frequency in the range from about 1 kHz to 10 kHz ispreferred. The amplitude of the output voltage of modulation source 120determines the amplitude of the AC variation (ripple) of the outputvoltage produced by amplifier 130A to which it is electricallyconnected. The instantaneous voltage gain of amplifier 130A iscontrolled by the sum of the DC output voltage of gain controller 125and the AC output voltage of modulation source 120, both of which areelectrically connected to the gain control terminal ofvoltage-controlled RF amplifier 130A by a summer or adder (notdepicted). FIG. 4 depicts modulation source 120 connected by theselector switch 175 to the control terminal of voltage-controlled RFamplifier 130A. The selector switch 175 can be an electronicallycontrolled device, rather than a mechanical device as depicted in FIG.4.

The output of voltage-controlled RF amplifier 130A is electricallycoupled to a match network 135A, which automatically matches the inputimpedance at the electrode segment 160A at the frequency determined byRF oscillator 105 using a match controller 170, and the output ofmatching network 135A is electrically connected to the power input port146A of directional coupler 145A. The power output port 147A ofdirectional coupler 145A is electrically connected to the input terminalof low-pass (or band-pass) filter 150A, which is intended to preventpower generated in the plasma at any harmonics of the RF frequencyproduced by RF oscillator 105 from reaching match network 135A. Finally,the output terminal of low-pass (or bandpass) filter 150A iselectrically connected to electrode segment 160A.

The amount of RF power emerging from electrode segment 160A is directedvia terminal 148A of directional coupler 145A to one terminal of aswitch 185. In fact, the RF signal emerging from terminal 148A ofdirectional coupler 145A is an attenuated RF voltage comprising a firstcomponent associated with the reflection of the RF signal incident onthe power coupling structure (i.e. electrode 160A) as well as additionalRF components associated with the coupling of RF power betweenelectrodes within the multi-electrode system. The switch 185 can be anelectronically controlled device, rather than a mechanical device asdepicted in FIG. 4. Corresponding terminals 148 of directional couplers145 are electrically connected, respectively, to corresponding terminalsof the switch 185. The RF power emerging from any electrode 160 can beconnected to the input terminal 195 of synchronous demodulator 140 byusing the switch 185. FIG. 4 depicts electrode segment 160A connected bythe switch 185 to the input terminal 195 of synchronous demodulator 140.

The reference terminal 190 of synchronous demodulator 140 is alsodepicted in FIG. 4 as electrically connected to the output of the masterRF oscillator 105. Although the demodulator of this embodiment is asynchronous demodulator 140, a simpler nonsynchronous demodulator may beused instead, albeit with somewhat reduced immunity to noise.

In addition, the amount of RF power incident upon electrode segment 160Afrom match network 135A may be measured at terminal 180A of directionalcoupler 145A (by using a detection system that is not depicted).

One such demodulator 140 could be an I-Q demodulator, wherein provided aRF input 195 and a local (reference) oscillator input 190, it outputstwo signals at the modulation frequency, namely, I(t)=I cos(ω_(m)t) andQ(t)=Q sin(ω_(m)t), where ω_(m) is the modulation frequency. Theamplitudes I and Q may be used to compute (I²+Q²)^(1/2) which isproportional to the desired power to be measured. When, for instance,selector switch 175 is set such that the RF signal incident on electrode160A is phase-modulated and selector switch 185 is set such that itreceives a RF signal from output 148A of directional coupler 145A, thenthe output (described above) from demodulator 140 is proportional to theRF power associated with the reflections of the corresponding RF powerincident at electrode 160A through match network 135A (and measured atnode 180A). Furthermore, while keeping the selector switch 175unchanged, selector switch 185 may be changed to receive the RF signalfrom output 148B of directional coupler 145B and then the output fromdemodulator 140 is proportional to the power coupled from electrode 160Ato electrode 160B. Similarly, this may be carried out through the Nthelectrode. Therefore, by carrying out this operation for each electrode,one may obtain N² outputs which, in addition to monitoring the reflectedincident power at each electrode (N signals), one also providessufficient information (the remaining N(N−1) signals) to understand thecoupling between electrodes of a N-electrode system as described in FIG.1.

Moreover, the output from the demodulator 140 (as described above) canbe calibrated (if necessary) by performing the N² measurements describedabove while only delivering RF power to a single electrode. For example,amplitude-modulated RF power is delivered to a first electrode (in themulti-electrode system) while sequentially recording the output fromdemodulator 140 for each selector switch 185 setting (i.e. eachelectrode) and, using a second directional coupler and detector (notshown) in line with the first directional coupler 145, sequentiallyrecording the power emerging from the respective electrode 160 in adirection from the electrode 160 to the match network 135. Simply byincreasing the power to the given electrode, one may increase thereflected power and power coupled to other electrodes, wherein acalibration curve for the output of demodulator 140 and power can beassembled. This sequence of measurements is then performed for each ofthe remaining electrodes. Moreover, the calibration may be repeatedwhile delivering power to multiple electrodes to check the significanceof nonlinear effects. Finally, a computer or processor 200 controls,using appropriate software, a phase controller 112, a gain controller125, a match controller 170, and, preferably, switches 175 and 185.Input to the computer 200 by an operator is affected by using an inputdevice 250, which is, for example, a keyboard or a touch-sensitivescreen. The computer 200 preferably includes a computer monitor 260, bywhich data obtained by the measurement system can be displayed. In oneembodiment, the computer 200 may serve to provide the match networkcontroller with the above-mentioned information, particularly themeasurement of the reflected incident power at each electrode. In turn,the match network controller may be programmed to minimize the reflectedincident power at each electrode and serve the purpose of providing arepeatable plasma process using the multi-electrode system. Similar tocontrollers in the prior art, this system provides information on theforward and reflected incident power at each electrode in amulti-electrode configuration to the control algorithm of the matchnetwork controller.

FIG. 5A is a diagram of an embodiment of the present invention depictinga phase modulation circuit with independent modulation sources for eachelectrode segment. The embodiment depicted in FIG. 5A is based on phasemodulation with a drive electrode having 3 segments. In general, theelectrode may include N segments. In the discussion of FIG. 5A thatfollows, the uppermost electrode segment is referred to as electrodesegment A. The circuit associated with electrode segment A, which isdenoted by 160A in FIG. 5A (and denoted generally by 22 in FIG. 2), willbe described. The circuits associated with the remaining N−1 electrodesegments (two additional electrode segments are shown in FIG. 5A) areidentical, and corresponding circuit elements are denoted by the samenumber with an appropriate letter appended after the number. All of theelectrode segments are immersed in plasma 270.

A master RF oscillator 105 from within the RF power supply system 26(see FIG. 2) provides a common RF signal as the input for the drivecircuit for each electrode segment. The power output and frequency of RFoscillator 105 is to be compatible with phase shifters 110, amplifiers130, and demodulator 140. The oscillator has a frequency that ispreferably 60 MHz, but other frequencies are possible. The power outputof the amplifiers 130 is typically of the order of hundreds of watts.

With regard to the drive circuit for electrode segment 160A, the outputof RF oscillator 105 is electrically coupled to the input terminal ofvoltage-controlled phase shifter 110A. The phase difference between theRF voltage at the output terminal of voltage-controlled phase shifter110A and the RF voltage at the input terminal of voltage-controlledphase shifter 110A is controlled by the sum of the output voltages ofphase controller 112 and modulation source 120A, both of which areelectrically connected to the phase control terminal of phase shifter110A by a summer or adder (not depicted). The phase difference isvariable over a range of 2π radians or, equivalently, 360°.

The frequency and amplitude of modulation voltage source 120A areadjustable, and a frequency in the range from about 1 kHz to 10 kHz ispreferred. In this embodiment, the frequencies of modulation sources120A, 120B, and 120C must be unique and the frequency ratios shouldpreferably not be rational numbers. The amplitude of the output voltageof modulation source 120A determines the amplitude of the AC phasevariation produced by phase shifter 110A to which it is electricallyconnected. The output terminal of phase shifter 110A is electricallycoupled to the input terminal of voltage-controlled RF amplifier 130A.The control terminal of voltage-controlled RF amplifier 130A iselectrically coupled to the output terminal of gain controller 125. Theoutput voltage of gain controller 125 controls the gain of thevoltage-controlled RF amplifier 130A.

The output of voltage-controlled RF amplifier 130A is electricallycoupled to match network 135A, which automatically matches the inputimpedance presented by the electrode segment 160A at the frequencydetermined by RF oscillator 105 by using a match controller 170, and theoutput of matching network 135A is electrically connected to the powerinput port 146A of directional coupler 145A. The power output port 147Aof directional coupler 145A is electrically connected to the inputterminal of low-pass (or band-pass) filter 150A, which is intended toprevent power generated in the plasma at any harmonics of the RFfrequency produced by RF oscillator 105 from reaching match network135A. Finally, the output terminal of low-pass (or band-pass) filter150A is electrically connected to electrode segment 160A.

The amount of RF power emerging from electrode segment 160A is directedvia terminal 148A of directional coupler 145A to one terminal of aswitch 185. In fact, the RF signal emerging from terminal 148A ofdirectional coupler 145A is an attenuated RF voltage comprising a firstcomponent associated with the reflection of the RF signal incident onthe power coupling structure (i.e. electrode 160A) as well as additionalRF components associated with the coupling of RF power betweenelectrodes within the multi-electrode system. The switch 185 can be anelectronically controlled device, rather than a mechanical device asdepicted in FIG. 5A. The respective terminals 148 of directionalcouplers 145 are electrically connected to respective terminals of theswitch 185. The RF power emerging from any electrode 160 can beconnected to the input terminal 195 of synchronous demodulator 140 byusing the switch 185. FIG. 5A depicts electrode segment 160A connectedby the switch 185 to the input terminal 195 of synchronous demodulator140.

The reference terminal 190 of synchronous demodulator 140 is alsodepicted in FIG. 5A as electrically connected to the output of themaster RF oscillator 105. The preferred demodulator for this embodimentis a synchronous demodulator 140, but a simpler non-synchronousdemodulator can be used instead, albeit with somewhat reducedsensitivity and immunity to noise.

In addition, the amount of RF power incident upon electrode segment 160Afrom match network 135A can be measured at terminal 180A of directionalcoupler 145A (by a detection system not depicted).

One such demodulator 140 could be an I-Q demodulator, wherein provided aRF input 195 and a local (reference) oscillator input 190, it outputstwo signals at the modulation frequencies, namely, I(t)=I_(a)cos(ω_(ma)t)+I_(b) cos(ω_(mb)t)+I_(c) cos(ω_(mc)t) and Q(t)=Q_(a)sin(ω_(ma)t)+Q_(b)sin(ω_(mb)t)+Q_(c)sin(ω_(mc)t), where ω_(ma), ω_(mb)and ω_(mc) are the modulation frequencies for each electrode 160A, 160Band 160C from modulation sources 120A, 120B and 120C, and I_(a), I_(b),I_(c), Q_(a), Q_(b) and Q_(c) are the corresponding amplitudes of therespective modulation frequencies in the I and Q signals. The signalsoutput from demodulator 140, I(t) and Q(t), may then be filtereddigitally within the computer processor 200 via Fourier analysis toextract a signal at each modulation frequency, or the I(t) and Q(t)signals may be filtered externally using an array of band-pass filters280 prior to A/D conversion at the computer processor 200 as shown inFIG. 5B. The amplitudes I_(j) and Q_(j) for the jth modulation frequencyω_(mj) may be used to compute (I_(j) ²+Q_(j) ²)^(1/2) which isproportional to the desired power to be measured. When, for instance,selector switch 185 is set such that it receives a RF signal from output148A of directional coupler 145A, then the amplitude (I_(a) ²+Q_(a)²)^(1/2) of filtered output at modulation frequency ω_(ma) (describedabove) from demodulator 140 is proportional to the RF power associatedwith the reflections of the corresponding RF power incident at electrode160A through match network 135A (and measured at node 180A), theamplitude (I_(b) ²+Q_(b) ²)^(1/2) of filtered output at modulationfrequency ω_(mb) from demodulator 140 is proportional to power fromelectrode 160B coupled to electrode 160A, and the amplitude (I_(c)²+Q_(c) ²)^(1/2) of filtered output at modulation frequency ω_(mc) fromdemodulator 140 is proportional to power from electrode 160C coupled toelectrode 160A. Similarly, this may be carried out through the Nthelectrode by changing the setting for selector switch 185. Therefore, bycarrying out this operation for each electrode, one may obtain N²outputs which, in addition to monitoring the reflected incident power ateach electrode (N signals), one also provides sufficient information(the remaining N(N−1) signals) to understand the coupling betweenelectrodes of a N-electrode system as described in FIG. 1.

Moreover, the output from the demodulator 140 (as described above) canbe calibrated (if necessary) by performing the N² measurements describedabove while only delivering RF power to a single electrode. For example,phase-modulated RF power is delivered to a first electrode (in themulti-electrode system) while sequentially recording the output fromdemodulator 140 for each selector switch 185 setting (i.e. eachelectrode) and, using a second directional coupler and detector (notshown) in line with the first directional coupler 145, sequentiallyrecording the power emerging from the respective electrode 160 in adirection from the electrode 160 to the match network 135. Simply byincreasing the power to the given electrode, one may increase thereflected power and power coupled to other electrodes, wherein acalibration curve for the output of demodulator 140 and power can beassembled. This sequence of measurements is then performed for each ofthe remaining electrodes. Moreover, the calibration may be repeatedwhile delivering power to multiple electrodes to check the significanceof nonlinear effects.

Finally, a computer or processor 200 controls, by using appropriatesoftware, a phase controller 112, a gain controller 125, a matchcontroller 170, and, perhaps, switches 175 and 185. Input to thecomputer 200 by an operator is affected by using an input device 250,which is, for example, a keyboard or a touch-sensitive screen. Thecomputer 200 includes a computer monitor 260, by which data obtained bythe measurement system is displayed. In one embodiment, the computer 200may serve to provide the match network controller with theabove-mentioned information, particularly the measurement of thereflected incident power at each electrode. In turn, the match networkcontroller may be programmed to minimize the reflected incident power ateach electrode and serve the purpose of providing a repeatable plasmaprocess using the multi-electrode system. Similar to controllers in theprior art, this system provides information on the forward and reflectedincident power at each electrode in a multi-electrode configuration tothe control algorithm of the match network controller.

FIG. 6 is a diagram of an alternative embodiment of the presentinvention depicting an amplitude modulation circuit with independentmodulation sources for each electrode segment. The embodiment of thepresent invention depicted in FIG. 6 is based on amplitude modulationwith a drive electrode having three segments. In general, the electrodeincludes N segments. In the discussion of FIG. 6 that follows, theuppermost electrode segment is referred to as electrode segment A. Thecircuit associated with electrode segment A, which is denoted by 160A inFIG. 6 (and denoted generally by 22 in FIG. 2), will be described. Thecircuits associated with the remaining N−1 electrode segments (twoadditional electrode segments are depicted in FIG. 6) are identical, andcorresponding circuit elements are denoted by the same number with anappropriate letter appended after the number. All of the electrodesegments are immersed in plasma 270.

A master RF oscillator 105 from within the RF power supply system 26(see FIG. 2) provides a common RF signal as the input for the drivecircuit for each electrode segment. The power output and frequency of RFoscillator 105 is compatible with phase shifters 110, amplifiers 130,and demodulator 140. The oscillator 105 has a frequency that ispreferably 60 MHz, but other frequencies are possible. The power outputof the amplifiers 130 is preferably on the order of hundreds of watts.

With regard to the drive circuit for electrode segment 160A, the outputof RF oscillator 105 is electrically coupled to the input terminal ofvoltage-controlled phase shifter 110A. The phase difference between theRF voltage at the output terminal of voltage-controlled phase shifter110A and the RF voltage at the input terminal of voltage-controlledphase shifter 110A is controlled by the output voltage of phasecontroller 112 which is electrically connected to the phase controlterminal of phase shifter 110A. The phase difference is variable over arange of 2π radians or, equivalently, 360°. The output terminal of phaseshifter 110A is electrically connected to the input terminal ofvoltage-controlled RF amplifier 130A.

In this embodiment, the frequencies of modulation sources 120A, 120B,and 120C must be unique and the frequency ratios should preferably notbe rational numbers. The amplitude of the output voltage of modulationsource 120 determines the amplitude of the AC variation (ripple) of theoutput voltage produced by amplifier 130A to which it is electricallyconnected. The instantaneous voltage gain of amplifier 130A iscontrolled by the sum of the DC output voltage of gain controller 125and the AC output voltage of modulation source 120A, both of which canbe electrically connected to the gain control terminal ofvoltage-controlled RF amplifier 130A by a summer or adder (notdepicted).

The output of voltage-controlled RF amplifier 130A is electricallycoupled to a match network 135A, which automatically matches the inputimpedance at the electrode segment 160A at the frequency determined byRF oscillator 105 by using a match controller 170, and the output ofmatching network 135A is electrically connected to the power input port146A of directional coupler 145A. The power output port 147A ofdirectional coupler 145A is electrically connected to the input terminalof low-pass (or band-pass) filter 150A, which is intended to preventpower generated in the plasma at any harmonics of the RF frequencyproduced by RF oscillator 105 from reaching match network 135A. Finally,the output terminal of low-pass (or bandpass) filter 150A iselectrically connected to electrode segment 160A.

The amount of RF power emerging from electrode segment 160A is directedvia a terminal 148A of directional coupler 145A to one terminal of aswitch 185. In fact, the RF signal emerging from terminal 148A ofdirectional coupler 145A is an attenuated RF voltage comprising a firstcomponent associated with the reflection of the RF signal incident onthe power coupling structure (i.e. electrode 160A) as well as additionalRF components associated with the coupling of RF power betweenelectrodes within the multi-electrode system. The switch 185 can be anelectronically controlled device, rather than a mechanical device asdepicted in FIG. 6. Corresponding terminals 148 of directional couplers145 are electrically connected, respectively, to corresponding terminalsof the switch 185. The RF power emerging from any electrode 160 can beconnected to the input terminal 195 of synchronous demodulator 140 byusing the switch 185. FIG. 6 depicts electrode segment 160A connected bythe switch 185 to the input terminal 195 of synchronous demodulator 140.

The reference terminal 190 of synchronous demodulator 140 is alsodepicted in FIG. 6 as electrically connected to the output of the masterRF oscillator 105. Although the demodulator of this embodiment is asynchronous demodulator 140, a simpler non-synchronous demodulator canbe used instead, albeit with somewhat reduced immunity to noise.

In addition, the amount of RF power incident upon electrode segment 160Afrom the match network 135A may be measured at terminal 180A ofdirectional coupler 145A (by a detection system not depicted).

One such demodulator 140 could be an I-Q demodulator, wherein provided aRF input 195 and a local (reference) oscillator input 190, it outputstwo signals at the modulation frequencies, namely, I(t)=I_(a)cos(ω_(ma)t)+I_(b) cos(ω_(mb)t)+I_(c) cos(ω_(mc)t) and Q(t) Q_(a)sin(ω_(ma)t)+Q_(b) sin(ω_(mb)t)+Q_(c) sin(ω_(mc)t), where ω_(ma), ω_(mb)and ω_(mc) are the modulation frequencies for each electrode 160A, 160Band 160C from modulation sources 120A, 120B and 120C, and I_(a), I_(b),I_(c), Q_(a), Q_(b) and Q_(c) are the corresponding amplitudes of therespective modulation frequencies in the I and Q signals. The signalsoutput from demodulator 140, I(t) and Q(t), may then be filtereddigitally within the computer processor 200 via Fourier analysis toextract a signal at each modulation frequency, or the I(t) and Q(t)signals may be filtered externally using an array of band-pass filters280 prior to A/D conversion at the computer processor 200 as shown inFIG. 5B. The amplitudes I_(j) and Q_(j) for the jth modulation frequencyω_(mj) may be used to compute (I_(j) ²+Q_(j) ²)^(1/2) which isproportional to the desired power to be measured. When, for instance,selector switch 185 is set such that it receives a RF signal from output148A of directional coupler 145A, then the amplitude (I_(a) ²+Q_(a)²)^(1/2) of filtered output at modulation frequency coma (describedabove) from demodulator 140 is proportional to the RF power associatedwith the reflections of the corresponding RF power incident at electrode160A through match network 135A (and measured at node 180A), theamplitude (I_(b) ²+Q_(b) ²)^(1/2) of filtered output at modulationfrequency ω_(mb) from demodulator 140 is proportional to power fromelectrode 160B coupled to electrode 160A, and the amplitude (I_(c)²+Q_(c) ²)^(1/2) of filtered output at modulation frequency ω_(mc) fromdemodulator 140 is proportional to power from electrode 160C coupled toelectrode 160A. Similarly, this may be carried out through the Nthelectrode by changing the setting for selector switch 185. Therefore, bycarrying out this operation for each electrode, one may obtain N²outputs which, in addition to monitoring the reflected incident power ateach electrode (N signals), one also provides sufficient information(the remaining N(N−1) signals) to understand the coupling betweenelectrodes of a N-electrode system as described in FIG. 1.

Moreover, the output from the demodulator 140 (as described above) canbe calibrated (if necessary) by performing the N² measurements describedabove while only delivering RF power to a single electrode. For example,amplitude-modulated RF power is delivered to a first electrode (in themulti-electrode system) while sequentially recording the output fromdemodulator 140 for each selector switch 185 setting (i.e. eachelectrode) and, using a second directional coupler and detector (notshown) in line with the first directional coupler 145, sequentiallyrecording the power emerging from the respective electrode 160 in adirection from the electrode 160 to the match network 135. Simply byincreasing the power to the given electrode, one may increase thereflected power and power coupled to other electrodes, wherein acalibration curve for the output of demodulator 140 and power can beassembled. This sequence of measurements is then performed for each ofthe remaining electrodes. Moreover, the calibration may be repeatedwhile delivering power to multiple electrodes to check the significanceof nonlinear effects.

Finally, a computer or processor 200 controls, by using appropriatesoftware, a phase controller 112, a gain controller 125, a matchcontroller 170, and, perhaps, switches 175 and 185. Input to thecomputer 200 by an operator is affected by an input device 250, whichis, for example, a keyboard or a touch-sensitive screen. The computer200 includes a computer monitor 260, by which data obtained by themeasurement system is displayed. In one embodiment, the computer 200 mayserve to provide the match network controller with the above-mentionedinformation, particularly the measurement of the reflected incidentpower at each electrode. In turn, the match network controller may beprogrammed to minimize the reflected incident power at each electrodeand serve the purpose of providing a repeatable plasma process using themulti-electrode system. Similar to controllers in the prior art, thissystem provides information on the forward and reflected incident powerat each electrode in a multi-electrode configuration to the controlalgorithm of the match network controller.

All of the embodiments described in FIGS. 3 through 6 may furtherinclude an isolator (or circulator with a load) connected to the outputof amplifier 130 and input of match network 135. The isolator canprotect the amplifier 130 from reflected RF power and RF power coupledfrom other electrodes.

With regard to the embodiments depicted in FIGS. 3-6, the match networkcomponents of a given circuit arm (e.g., 135A) can be adjusted via inputto the match network controller 170 from the computer 200 (and from thedemodulator 140) to reduce the reflected power at electrode 160Aassociated with a reflection of the power incident on the electrode 160Afrom a signal generated by oscillator 105 and amplified by amplifier130A. In other words, the apparatus and methods described in the abovedisclosed embodiments are capable of dissecting the RF power measured atcoupler 180 and dissociating the reflected “incident” signal from thosesignals associated with coupling from the other electrodes. In thismanner, a repeatable impedance match can be obtained for each electrodein a multi-electrode system, which can, in turn, contribute torepeatable process results.

It should be noted that the exemplary embodiments depicted and describedherein set forth the preferred embodiments of the present invention, andare not meant to limit the scope of the claims hereto in any way.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. An apparatus for improved impedance matching between an RF signal anda multi-segmented electrode in a plasma reactor powered by the RFsignal, said apparatus comprising an electrode segment adapted to beconnected to the RF signal by a circuit comprising: a phase shifteradapted to be connected to the RF signal; an amplifier connected to anoutput of said phase shifter; a matching network connected to an outputof said amplifier, said matching network being configured to match animpedance of the amplifier with an impedance of said electrode segment;a modulation source configured to modulate the RF signal prior toreceipt by said matching network; a directional coupler connected to anoutput of said matching network, said directional coupler having anoutput connected to said electrode segment; a demodulator beingconfigured to receive an output signal from said directional coupler anda reference signal; and a control system connected to an output of saiddemodulator, said control system being configured to control saidmatching network such that said output signal of said directionalcoupler and said reference signal produce a signal of substantiallyminimized amplitude.
 2. The apparatus according to claim 1, wherein saidmodulation source is connected to an input terminal of said phaseshifter.
 3. The apparatus according to claim 1, wherein said modulationsource is connected to an input terminal of said amplifier.
 4. Theapparatus according to claim 1, wherein said modulation source isadjustable.
 5. The apparatus according to claim 1, wherein saidreference signal is received by said demodulator from said master RFoscillator.
 6. The apparatus according to claim 1, wherein saiddemodulator is synchronous.
 7. The apparatus according to claim 1,wherein said demodulator is non-synchronous.
 8. The apparatus accordingto claim 1, wherein said control system is configured to control saidphase shifter and said amplifier.
 9. The apparatus according to claim 1,further comprising a filter connected to an output of said directionalcoupler, said filter having an output connected to said electrodesegment.
 10. The apparatus according to claim 1, further comprising anadditional electrode segment adapted to be connected to the RF signal bysaid circuit, said circuit further comprising: an additional phaseshifter adapted to be connected to the RF signal; an additionalamplifier connected to an output of said additional phase shifter; anadditional matching network connected to an output of said additionalamplifier, said additional matching network being configured to match animpedance of the additional amplifier with an impedance of saidadditional electrode segment; said modulation source being selectivelyconfigured to modulate the RF signal prior to receipt by said additionalmatching network; an additional directional coupler connected to anoutput of said additional matching network, said additional directionalcoupler having an output connected to said additional electrode segment;said demodulator being configured to selectively receive an outputsignal from said additional directional coupler and an additionalreference signal representing the RF signal at the output of said masterRF oscillator; and said control system being configured to control saidoutput of said additional matching network such that said output signalof said additional directional coupler and said additional referencesignal sent via said demodulator produce a signal of substantiallyminimized amplitude.
 11. The apparatus according to claim 1, furthercomprising an additional electrode segment adapted to be connected tothe RF signal by said circuit, said circuit further comprising: anadditional phase shifter adapted to be connected to the RF signal; anadditional amplifier connected to an output of said additional phaseshifter; an additional matching network connected to an output of saidadditional amplifier, said additional matching network being configuredto match an impedance of the RF signal with an impedance of saidadditional electrode segment; an additional modulation source configuredto modulate the RF signal prior to receipt by said additional matchingnetwork; an additional directional coupler connected to an output ofsaid additional matching network, said additional directional couplerhaving an output connected to said additional electrode segment; saiddemodulator being configured to receive an output signal from saidadditional directional coupler and an additional reference signalrepresenting a RF signal at the output of said master RF oscillator; andsaid control system connected to said output of said demodulator, saidcontrol system being configured to control said output of saidadditional matching network such that said output signal of saidadditional directional coupler and said additional reference signal sentvia said demodulator produce a signal of substantially minimizedamplitude.
 12. An apparatus for improved impedance matching between anRF signal and a multi-segmented electrode in a plasma reactor powered bythe RF signal, said apparatus comprising an electrode segment adapted tobe connected to the RF signal by a circuit comprising: a phase shifteradapted to be connected to the RF signal; an amplifier connected to anoutput of said phase shifter; a matching network connected to an outputof said amplifier, said matching network being configured to match animpedance of the amplifier with an impedance of said electrode segment;a modulation source configured to modulate the RF signal prior toreceipt by said matching network; a directional coupler connected to anoutput of said matching network, said directional coupler having anoutput connected to said electrode segment; and means for adjusting saidoutput of said match network such that an output signal from saiddirectional coupler and a reference signal from a RF signal at theoutput of said master RF oscillator produce a signal of substantiallyminimized amplitude.
 13. A plasma reactor comprising: a process chamber;a multi-segmented electrode within said process chamber; a RF powersupply system configured to generate a RF signal to drive an electrodesegment of said multi-segmented electrode; and a circuit connecting saidelectrode segment to said RF signal, and circuit comprising: a phaseshifter adapted to be connected to said RF signal, a matching networkconnect to an output of said amplifier, said matching network beingconfigured to match an impedance of said amplifier with an impedance ofsaid electrode segment, a modulation source configured to modulate saidRF signal prior to receipt by said matching network, a directionalcoupoler connected to an output of said matching network, saiddirectional coupler having an output connected to said electrodesegment, a demodulator being configured to receive an output signal frmsaid directional coupler and a reference signal representing a RF signalat the output of said master RF oscillator, and a control systemconnected to an output of said demodulator, said control system beingconfigured to control said output of said matching network such thatsaid output signal of said directional coupler and said reference signalsent via said demodulator produce a signal substantially minimizedamplitude.
 14. An apparatus for improved impedance matching between anRF signal and a multi-electrode plasma reactor powered by the RF signal,said apparatus comprising at least one electrode adapted to be connectedto the RF signal by a circuit comprising: a phase shifter adapted to beconnected to the RF signal; am amplifier connected to an output of saidphase shifter; a matching network connected to an output of saidamplifier, said matching network being configured to match an impedanceof the amplifier with an impedance of said electrode; a modulationsource configured to modulate the RF signal prior or to receipt by saidmatching network; directional coupler connected to an output of saidmatching network, said directional coupler having an output connected tosaid electrode; demodulator being configured to receive an output signalfrom said directional coupler and a reference signal representing a RFsignal at the output of the master RF oscillator; and control systemconnected to an output of said demodulator, said control system beingconfigured to control said output of said matching network such thatsaid output signal of said directional coupler and said reference signalsent via said demodulator produce a signal of substantially minimizedamplitude.
 15. A method according to claim 14, wherein said electrodecomprises at least one of a plate electrode, an electrode segment, andan inductive cell.